1. Field of the Invention
The present invention relates to thermal type infrared ray detector with a thermal separation structure.
2. Description of the Related Art
As an infrared ray detecting device, a detecting device of a thermal separation structure is known as xe2x80x9cMonolithic Silicon Micro-bolometer Arraysxe2x80x9d in xe2x80x9cUncooled Infrared Imaging Arrays and Systemsxe2x80x9d by R. A. Wood, (Semiconductors and Semimetals, Volume 47, volume editors P. W. Kruse and D. D. Skatrud, Academic Press, 1997, p103). FIGS. 1 and 2 show such a thermal separation structure of a picture element of a bolometer type uncooled infrared sensor array. As shown in FIGS. 1 and 2, a readout circuit 102 for bolometer is formed in a Si substrate 101, and a diaphragm 105 is supported by two beams 104 to form an air gap 103 between a semiconductor 101 and the diaphragm 105. The structure material of the beam 104 is a protective insulating film 106 of silicon nitride and the thickness of a wiring line film which is formed of NiCr on the beam 104 is 50 nm. The diaphragm 105 as a light receiving section is composed of a thin film 107 of vanadium oxide with the resistance of 20 kxcexa9 as a bolometer material and a protective insulating film 106 of silicon nitride with the thickness of 800 nm. A full reflection film 108 is formed on the surface of the readout circuit 102 through the protective insulating film.
When infrared rays 109 are incident on the diaphragm 105 in such a thermal separation structure, the infrared rays 109 are absorbed by the silicon nitride thin film 106. A part of the infrared rays 109 passes through the diaphragm 105 and then is reflected to the direction of the diaphragm 105 by the reflection film 108. Thus, the reflected infrared rays are absorbed once again by the silicon nitride thin film 106. In this way, the infrared rays are absorbed so that the temperature of the diaphragm 105 changes. The resistance of the bolometer thin film 107 changes through the change of the temperature, and is converted into a voltage change by the readout circuit. Thus, an infrared picture is obtained.
Also, as the infrared ray detecting device, a bolometer type noncooled infrared sensor array by H. Wada et al., (SPIE Vol. 3224, 1997, p40) is known. FIGS. 7 and 8 show a thermal separation structure of a picture element of the bolometer type noncooled infrared sensor array. FIG. 3 is a plan view showing the picture element, and FIG. 4 is a sectional view of the picture element along a broken line shown by a point line of A1-A2-A3-A4-A5-A6-A7-A8-A9-A10. A diaphragm 113 is supported by two beams 112 to form an air gap between the diaphragm 113 and a silicon substrate 111 with a readout circuit. The structure material of the beam 112 is a protective insulating film 114 of silicon nitride, and a wiring line material 115 of the beam 112 is a Ti film having the thickness of 100 nm. The diaphragm 113 as a light receiving section is formed of a vanadium oxide thin film 116 with the sheet resistance of 10 to 30 kxcexa9/sq as bolometer material, an protective insulating film 117 of silicon nitride with the thickness of 400 nm and an infrared absorption film 118 of TiN thin film with the thickness of 15 nm.
The wiring line 115 on the beam 112 is connected with the readout circuit in the silicon substrate 111 by wiring line plugs 121 through a contact 120 provided in a bank section 119. Also, a reflection film 122 of a WSi film with the thickness of 20 nm and a protective insulating film 123 are formed on the silicon substrate through a thermal oxidation film.
The distance between the reflection film 122 and the infrared absorption film 118 is adjusted to 1/(4n) of the wavelength of an infrared ray to be detected (n is effective refractive index). The infrared rays are absorbed by the infrared absorption film 118. A part of the infrared rays passes through the infrared absorption film 118, and then are reflected by the reflection film 122 to the direction of the diaphragm 113. In the diaphragm 113, the infrared rays interfere with each other so that a component of the infrared rays with the wavelength to be detected is absorbed by the infrared absorption film 118. Thus, change of the temperature of the diaphragm is caused. The resistance of the bolometer thin film 116 changes through the change of the temperature, and the change of the resistance is converted into a voltage change by the readout circuit. In this way, an infrared picture is obtained.
Also, as the infrared ray detecting device, a micro-bolometer array by Cunningham et al., (U.S. Pat. No. 5,688,699) is known. FIG. 5 shows a thermal separation structure of a picture element of the micro-bolometer array. As shown in FIG. 5, an epitaxial layer 131 is grown on a silicon substrate 130, and a readout circuit for the bolometer is formed in the epitaxial layer 131. A diaphragm 133 is provided above the epitaxial layer 131 and is supported by two beams 132 and 132xe2x80x2 to form an air gap between the diaphragm 133 and the epitaxial layer 131.
The structure material of the beam 132 or 132xe2x80x2 is silicon nitride 134, and a wiring line 135 on the beam 132 or 132xe2x80x2 is formed of a Cr film with the thickness of 10 nm and a Ni film with the thickness of 20 nm. The diaphragm 133 as a light receiving section is formed of a vanadium oxide thin film 136 of bolometer material with the sheet resistance of 15 to 30 kxcexa9. Also, the diaphragm 133 is further composed of a protective insulating film 137 of silicon nitride with the thickness of 100 nm and an infrared absorption film of a gold thin film having the thickness of 10 nm. In FIG. 5, the absorption film is not shown.
The diaphragm 133 and wiring line films are electrically connected by contact sections 138a and 138b formed of the bolometer material. Also, the wiring line films and the readout circuit in the epitaxial layer are electrically connected by a contact 139. Also, the epitaxial layer 131 is covered by a SiO2 protective insulating film 140 and a reflection film composed of a Pt film with the thickness of 50 nm and a Cr film with the thickness of 5 nm. In FIG. 5, a reflection film is not shown.
The distance between the reflection film and the infrared absorption film is adjusted to xc2xcn of a detection wavelength (n: effective refractive index). The infrared rays absorbed by the infrared absorption film and the infrared rays passing through the infrared absorption film and then reflected by the reflection film to the direction of the diaphragm interfere with each other. As a result, the infrared rays with the detection wavelength are absorbed by the infrared absorption film, so that the temperature of the diaphragm changes. The resistance of the bolometer thin film changes through the change of the temperature, and the change of the resistance is converted into a voltage change by the readout circuit. In this way, an infrared picture is obtained.
Also, as the infrared ray detecting device, a pyroelectric-type array by Hanson et al., (SPIE vol. 3379, 1998, p60) is known. FIGS. 6 and 7 are a thermal separation structure of a picture element of the pyroelectric type array. As shown in FIGS. 6 and 7, a diaphragm 152 is supported by two beams 151 to form an air gapxe2x80x2 between the diaphragm 152 and a silicon substrate 150 with a readout circuit. The diaphragm 152 is composed of a lower electrode 153 of Pt/Ti, a pyroelectric thin film 154 of (Pb,La)(Zr,Ti)O3 with the thickness of 250 to 350 nm on the electrode 153 and an upper electrode 155 of a Nickel-Chrome thin film. One of the two beams 151 is composed of the lower electrode 153 and the pyroelectric thin film 154, and the other beam 151 is composed of the pyroelectric thin film 154 and the upper electrode 155. The thermal conduction of such a well known thermal separation structure of is determined based on Pt of the lower electrode.
The upper electrode and the lower electrode are connected with the readout circuit in the silicon substrate 150 through contacts 156. The infrared rays are incident on the diaphragm 152, and interfere between the upper electrode and the lower electrode to cancel each other. As a result, the infrared rays with a specific wavelength are absorbed by the upper electrode, so that the temperature of the diaphragm changes. The surface electric charge quantity of the pyroelectric thin film 154 changes in accordance with the change of the temperature and the change of the charge quantity is converted into a voltage change by the readout circuit. In this way, an infrared picture is obtained.
The fact will be considered that the sensitivity of the thermal type infrared sensor of the above conventional examples is proportional to a fill factor. The fill factor is the ratio of the diaphragm as a light receiving section to a picture element. The wiring lines such as a signal line extend on a bank section 119 in the conventional example shown in FIGS. 3 and 4. Therefore, the fill factor of the diaphragm as the light receiving section can not be made large in the conventional example. For this reason, it is desirable that these wiring lines are arranged under the diaphragm to improve the sensitivity of the detector.
Also, the factor will be considered that the sensitivity of the conventional example of the thermal type infrared sensor is inversely proportional to a thermal conductance to be described later. The wiring line material and the structure material of the beam in the above four conventional examples are as follows: a NiCr film with the thickness of 800 nm and a silicon nitride thin film having the thickness of 50 nm in FIGS. 1 and 2; a Ti film with the thickness of 100 nm and the multiple thin film of silicon nitride and silicon oxide the total thickness of about 600 nm in FIGS. 3 and 4; a layer structure wiring line of a Cr film with the thickness of 10 nm and a Ni film with the thickness of 20 nm and the silicon nitride film in FIG. 5; and one of the beams composed of the Ti and Pt thin film and the ferroelectric thin film of 30 to 60 nm, and the other beam is composed of NiCr thin film and a ferroelectric thin film in FIGS. 6 and 7. In case of FIGS. 6 and 7, the thermal conductance is determined depending on the Pt thin film. Therefore, it is desired to select an optimal material for the wiring line material to improve the sensitivity of the detector.
In conjunction with the above description, a thermal type infrared ray sensor is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-19671). In this reference, the infrared sensor 20 formed above a semiconductor substrate 1 is composed of an infrared light receiving section 21 and bridge sections 24. The infrared light receiving section 21 converts incident infrared rays into a thermal energy and electrically outputs the physical value changing in accordance with the converted thermal energy. A wiring line layer 24A is provided for the bridge section 24 to electrically connect the infrared light receiving section and the semiconductor substrate 1. At least one the above infrared light receiving section 21 and the bridge section 24 is supported by insulative leg sections 25, 26 and 27. The reduction of thermal conductance between the infrared light receiving section 21 and/or the bridge section 24 and the semiconductor substrate 1 is attempted.
Also, an infrared solid imaging device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-332480). In this reference, in a 2-dimensional infrared ray solid imaging device using a thermal infrared ray detector, a thermal type light detector section is supported on a semiconductor substrate by support legs with large thermal resistance. The temperature change of the thermal type detector section on the incidence of infrared rays is detected through the wiring lines in the support leg. A plurality of wiring lines are arranged in parallel or laminated in at least one support leg.
Also, an infrared detector is disclosed in Japanese Patent No. 2,834,202 corresponding to U.S. patent application No. 231,797 filed on Aug. 12, 1988. In this reference, a bolometer array for detecting radiation in an infrared spectrum range is composed of a substrate including an array of bolometer circuit element sets in the neighborhood of the surface of the substrate. An array of resistances is distanced from the surface by xc2xc of the wavelength in the center of the infrared ray radiation spectral range. Each of the resistances and leads of the resistances is composed of a stack, which includes a first conductive layer, a resistance layer and a second conductive layer. The second conductive layer is the nearest the surface. Each of the resistances is oriented to receive the radiation, and provided above a corresponding one of the bolometer circuit sets to be electrically connected with the corresponding. bolometer circuit set. The sheet resistances of the first conductive layer and the second conductive layer causes at least 50% of absorption in the said spectral range. Also, the bolometer array includes a chopper for chopping the radiation to the said resistance. The second conductive layer has an inactive layer, and the surface is reflective. The space between the surface and the inactive layer is exhausted. The stack contains a first inactive layer on the first conductive layer and a second inactive layer on the second conductive layer. The first inactive layer and the second inactive layer are formed of silicon dioxide. The first conductive layer and the second conductive layer are formed of titanium nitride. The resistance layer is formed of amorphous silicon.
Therefore, an object of the present invention is to provide a thermal type infrared ray detector with a thermal separation structure, in which a fill factor can be increased.
Another object of the present invention is to provide a thermal type infrared ray detector with a thermal separation structure, in which a wiring line is arranged under a diaphragm.
Still another object of the present invention is to provide a thermal type infrared ray detector with a thermal separation structure, in which the sensitivity of the detector can be improved by selecting an optimal material.
In order to achieve an aspect of the present invention, a thermal type infrared ray detector with a thermal separation structure includes a plurality of picture elements, each of which includes a circuit formed in a substrate for every picture element, and a light receiving section converting infrared rays into change of a resistance or a charge quantity. The circuit generates a voltage signal from the resistance change or the charge quantity change. Beams mechanically support the light receiving section from the substrate to form a gap between the light receiving section and the substrate, and electrically connect the light receiving section to the circuit. Each of the beams includes a wiring line film formed of Ti alloy and connecting the light receiving section to the circuit, and a protective insulating film surrounding the wiring line film. In this case, the Ti alloy may be TiAl6V4.
Also, the light receiving section may be connected to the circuit via contact pads. In this case, it is desirable that the contact pad for a first of the plurality of picture elements and the contact pad of a second of the plurality of picture elements which is disposed in a diagonal direction from the first picture element are structurally unified and electrically insulated.
Also, it is desirable that a signal line for transferring the voltage signal to the circuit and a ground line are formed in the substrate.
Also, the thermal type infrared ray detector may further include a reflecting film formed on the substrate to perfectly reflect the infrared ray which has passed through the light receiving section, toward the light receiving section.
Also, the converting film may include a bolometer material film. In this case, the light receiving section may further include a protective insulating film formed to cover the bolometer material film.
Instead, the light receiving section may include a lower electrode, a ferroelectric material thin film formed on the lower electrode, and an upper electrode formed on the ferroelectric material thin film. In this case, the light receiving section may further include a protective insulating film formed to cover the upper electrode.
In order to achieve another aspect of the present invention, a thermal type infrared ray detector with a thermal separation structure includes a plurality of picture elements, each of which includes a circuit formed in a substrate for every picture element, and a light receiving section converting infrared rays into change of a resistance or a charge quantity. The circuit generates a voltage signal from the resistance change or the charge quantity change. Beams mechanically support the light receiving section from the substrate to form a gap between the light receiving section and the substrate, and electrically connect the light receiving section to the circuit. Each of the beams includes a wiring line film formed of Ti alloy and connecting the light receiving section to the circuit, and a protective insulating film surrounding the wiring line film. Also, a signal line for transferring the voltage signal to the circuit and a ground line are formed in the substrate. In this case, it is desirable that the Ti alloy is TiAl6V4.
Also, the light receiving section may be connected to the circuit via contact pads. In this case, it is desirable that the contact pad for a first of the plurality of picture elements and the contact pad of a second of the plurality of picture elements which is disposed in a diagonal direction from the first picture element are structurally unified and electrically insulated.
Also, the thermal type infrared ray detector may further include a reflecting film formed on the substrate to perfectly the infrared ray which has passed through the light receiving section, toward the light receiving section.
Also, the converting film may include a bolometer material film. In this case, the light receiving section may further include a protective insulating film formed to cover the bolometer material film.
Instead, the light receiving section may include a lower electrode, a ferroelectric material thin film formed on the lower electrode, and an upper electrode formed on the ferroelectric material thin film. In this case, the light receiving section may further include a protective insulating film formed to cover the upper electrode.
In order to achieve still another aspect of the present invention, a thermal type infrared ray detector with a thermal separation structure includes a plurality of picture elements, each of which includes a circuit formed in a substrate for every picture element, and a light receiving section converting infrared rays into change of a resistance or a charge quantity. The circuit generates a voltage signal from the resistance change or the charge quantity change. Beams mechanically support the light receiving section from the substrate to form a gap between the light receiving section and the substrate, and electrically connecting the light receiving section to the circuit via contact pads. Each of the beams includes a wiring line film formed of Ti alloy and connecting the light receiving section to the circuit, and a protective insulating film surrounding the wiring line film. The contact pad for a first of the plurality of picture elements and the contact pad of a second of the plurality of picture elements which is disposed in a diagonal direction from the first picture element are structurally unified and electrically insulated. In this case, it is desirable that the Ti alloy is TiAl6V4.
Also, it is desirable that a signal line for transferring the voltage signal to the circuit and a ground line are formed in the substrate.
Also, the thermal type infrared ray detector may further include a reflecting film formed on the substrate to perfectly reflect the infrared ray which has passed through the light receiving section, toward the light receiving section.
Also, the converting film may include a bolometer material film. In this case, the light receiving section may further include a protective insulating film formed to cover the bolometer material film.
Instead, the light receiving section may include a lower electrode, a ferroelectric material thin film formed on the lower electrode, and an upper electrode formed on the ferroelectric material thin film. In this case, the light receiving section may further include a protective insulating film formed to cover the upper electrode.